The long term goal of this proposal is directed at understanding two aspects of balance in individuals diagnosed with bilateral vestibular loss and non-vestibular loss subjects. First, how is vestibular and visual information used by the central nervous system to modify balance responses when the goal of a task remains constant but environmental conditions change. First, how is vestibular and visual information used by the central nervous system to modify balance responses when the goal of a task remains constant but environmental conditions change. Second, how many vestibular and visual information contribute to the intentional modification of goal-oriented balance responses. The proposed experiments will explore the emergence of balance patterns under the conditions of a platform that moves sinusoidally at varying frequencies. In experiments studying sinusoidal translation from humans standing upright, it was observed that individuals ride with the platform for frequencies less than or equal to 0.5 Hz and fix their head in space relative to the moving platform for frequencies greater than 0.5 Hz. Thus, two distinct balance patterns emerge as a function of environmental conditions, with similar behavior observed with the eyes opened or closed. Individuals with bilateral vestibular loss produce similar balance patterns with the eyes open, but tend to loss orientation in the form of stepping as the platform moves at frequencies greater than 0.5 Hz. In the above experiments, platform frequency was established as an initial condition. Will spontaneous switching between the two balance patterns occur when platform frequency is parametrically scaled from slow (0.25 Hz) to fast (1.0 Hz) frequencies in a single trial? Are subjects capable of establishing either balance pattern at any frequency when intentionally instructed to do so? How is vestibular and visual information used to achieve stable balance patterns in such tasks? Through the study of joint angle patterns, muscle patterns and force patterns our understanding of the role of vestibular and visual information, as well as intention, on the production of stable balance patterns will be enhanced. Moreover, the results of the project will provide experimental protocols for the evaluation and rehabilitation of individuals with neurological impairments that affect the production of stable balance and gait patterns,